Inclinometers



kot.7,1958 G. P. WRIGHT 2,854,762

' INGLINOMETERS Filed April 2, 1956 Sx i FIG. 4. 8

' Cx? RlctH-v INVEN TOR BY @Ww/Mw ATTO EY5 United tates Patent O 2,854,762 iNeLrNoMnrEn's Gordon I. Wright, Hiliington, Giasgow, Scotland, assignor to Keivn ik Hughes Limited, Glasgow, Scotland Application April 2, 1956, Serial No. $190,453.?.

1 Claim. (Ci. E53-7.06)

This invention relates to inclinometers especially for aircraft turn and slip'indicators.

It has been known to arrange the inclinometer or slip tube of a turn and slip indicator so that slip is indicated by means of a black sphere moving against an illuminated background. Particularly in night ying, this gives rise to a certain amount of fatigue as the pilot is constantly faced with an appreciable area of bright light from this background.

According to the present invention there is provided an inclinometer wherein the inclination is indicated by an illuminated or luminous sphere moving against a darkened background of the inclinometer tube.

lt is further proposed that the said sphere should be transparent and be backed with a fluorescent or phosphorescent compound so that in effect there is only a point source of light.

Such spheres have proved to be difficult to make, but a satisfactory sphere for use in an inclinometer can be made.

The sphere will now be further described by way of example.

A hollow hemisphere of glass, with a wall of 20 to 40 thousandths of an inch thickness, has a slightly rough inner or concave surface produced by sand blasting or other means and a ground and polished outer or convex surface. This hemisphere is filled with a fluorescent or phosphorescent compound which is pressed firmly into position and so filling the hollow of the hemisphere. It has been found that a suitable compound for this purpose is a zinc cadmium sulphide fluorescent pigment. The Surface of the compound which is packed into the hemisphere is smooth and level with the edge of the hemisphere. The above described hemisphere and another hemisphere identical to it are fixed together in the form of a sphere by means of a polymerising optical cement. The optical cement may be a low viscosity blue optical cement such as an epoxy resin which is similar to Araldite 15. The cemented sphere is heat treated so as to cause the cement to polymerise thus forming a permanent seal between the two hemispheres.

Reference is made to the drawings which are presented for illustrative purposes only and are not to be taken as limiting. Like numerals refer to like parts throughout.

Figure 1 is a front elevation of one form of inclinometer assembly embodying the invention.

Figure 2 is a perspective view of Figure 1.

Figure 3 is a plan view of Figure 1.

Figure 4 is anV enlarged perspective view of the construction of the luminous sphere of Figure 1.

The hollow luminous sphere comprises two transparent hemispheres 7 and 8, filled with a fluorescent or phosphorescent material 9 which may be zinc cadmium sulphide fluorescent pigment which is in intimate contact with the inner surface of the hemispheres 7 and 8, which have been roughened by sand blasting or the like to improve contact and adherence between the luminous'material 9 and the inner surfaces. The lled hemispheres 7 and 8, with their contents 9, are adhered together by a suitable polymerizing optical cement and the assembled parts heat treated to form a permanent seal, joining the two halves 7 and 8 and their contents 9.

The outer surface of the sphere is ground and polished with accuracy so that the sphere will move readily for small inclinations. In addition, a sphere of relatively low mass is preferred to limit the effects of inertia so the sphere will respond readily to acceleration forces, but will not over run. To achieve this result the wall thickness is held to between twenty and forty-thousands of an inch. The luminescent compound is substantially lighter than an equal volume of glass. This lightness of the sphere makes the sphere highly responsive and at the same time makes the damping action of the liquid 6 more effective.

An added advantage of the thin-walled sphere is that it tends to maximize the size of the effective luminous area of the sphere to the pilot or other observer.

The completed sphere is placed in an inciinoineter assembly comprising a tube 1, which is slightly'larger than the luminous ball which is free to roll therein. Tube 1 is curved as shown, so that the ball 7, S normally rests midway between the ends 2 and 3.

Tube 1 is sealed as at 5 and lled with a suitable damping liquid 4, which causes the ball 7, 8 to move slowly within the tube l under the action of gravity and/ or other forces of acceleration. Tube 1 has hollow upstanding arm portion 6 into which the damping liquid 4 extends, thus assuring that the curved body portion of tube 1 is lled, and also allowing for the expansion of the damping liquid due to changes in temperature. The back wall of the curved tube 1 is painted black or otherwise coated as at 10 to provide a darkened background against which the luminous sphere stands out distinctly. As the tube 10 is inclined in space the luminous ball 7, 8, 9 moves to the lowest part of the curve. 'The amount of displacement from the center is a measure of the inclination of the tube.

While there has been described above what are presently believed to be the preferred forms of the invention, variations thereof will be obvious to those skilled in the art; and all such changes and variations which fall within the spirit of the invention are intended to be covered by the generic terms in the appended claim, which are variably worded to that end.

I claim:

in combination, an inclinometer having a substantially transparent tube having a darkened background, a luminous sphere within said tube and movable along said tube, said luminous sphere comprising two sections forming a hollow sphere containing luminous material in contact with the inside of said sphere, said sections comprising hollow hemispheres of transparent glass cemented into a sphere by a polymerizing optical cement, said hemispheres having a wall thickness between 20 yand 40 thousandths of an inch, a rough inner concave surface and a ground and polished outer convex surface.

References Cited in the tile of this patent UNITED STATES PATENTS 1,077,305 Rosenheim Nov. 4, 1913 1,330,180 Erdle Feb. 10, 1920 1,395,110 Hole Oct. 25, 1921 2,353,586 Reininger July l1, 1944 FOREIGN PATENTS 29,677 Great Britain Dec. 21, 1910 

